Phosphorus trifluoride is a chemical compound having the chemical formula PF3. It exists as a colorless and odorless gas at room temperature. It is highly toxic in nature. Many students may have doubts regarding whether PF3 is polar or not. In this article, we will discuss this and also cover its properties and applications.
So, Is PF3 Polar or Nonpolar? PF3 is a polar molecule. Phosphorus and fluorine have different electronegativity and the PF3 molecule also contains a lone pair. As a result, the shape of the molecule is trigonal pyramidal and it ensures a non zero dipole moment making the PF3 a polar molecule.
Phosphorus trifluoride is a toxic substance and is odorless and colorless in appearance. It is widely used as a ligand in various metal complexes.
Phosphorus trifluoride is prepared from the phosphorus trichloride by the process of halogenation exchange of various fluoride compounds like Xinc fluoride, calcium fluoride, etc.
Below is a reaction of preparation of PF3 by halogen exchange process by ZnF2
2PCl3 + 3ZnF2 ———-> 2 PF3 (Phosphorus trifluoride) + 3ZnCl2
If we talk about the chemical composition of PF3, the molecule consists of one phosphorus atom and three fluorine atoms.
The valence electrons of Phosphorus are 5 and fluorine has 7 valence electrons in its outermost shell.
The molecular mass of PF3 is calculated as
Mol mass of PF3 = 1 * 30 (mol mass of P) + 3 * 18.9 (mol mass of F) = 87.96 g/mol.
In the molecule of PF3, the phosphorus atom is the central atom surrounded by three fluorine atoms. Fluorine needs one electron to complete its octet.
Therefore, three fluorine atoms form a covalent bond with phosphorus leaving behind one lone pair on phosphorus atom.
The electronegativity of fluorine is 3.98 and that of Phosphorus is 2.19. Due to this difference between their electronegativity, the P-F bond is polar.
As a result, all the P-F bonds ensure non zero dipole moment in the same direction.
Due to the lone pair present on phosphorus atom, the bonds face a repulsive force in a downward direction due to repulsion between lone pair and bond pairs.
As a result, the dipole moment of the entire molecule is non zero making the PF3 a polar molecule.
What are Polar and Nonpolar Molecules?
The molecules are held by the interatomic forces. The types of forces that held the toms are covalent, ionic, metallic, and hydrogen bonds.
The covalent and ionic bonds have the greatest strength among all the types of bond forces. The polar molecules have covalent bonding in it.
Covalent bonds can be polar and nonpolar depending upon several factors like electronegativity, geometrical shape, and dipole of the molecule.
Polar Molecules: The molecules that have their dipole moment equal to non zero are polar molecules.
These molecules have unequal charge distribution on their atoms. This is because of the difference between the electronegativity of the atoms in a polar molecule.
The covalent bond formed by two atoms is said to be polar if the atoms differ in their electronegativity.
More electronegative atom attracts the bonded charge slightly towards itself and gains a partial negative charge.
As a result, other atom gains partial positive charge and two poles originate across a molecule.
Few examples of such molecules are H2O, OF2. You can check out the reason for the polarity of OF2.
Nonpolar Molecules: These molecules have zero dipole moment. In such molecules, the atoms have an equal distribution of charge.
The covalent bond formed by two atoms forms a nonpolar bond if they share an equal proportion of charge.
Both atoms have equal influence on the bonded pair of electrons. No poles generate across the molecule.
Few examples of such molecules are Br2, Hexane. You can check out the reason for the non-polarity of hexane.
Why is PF3 a polar molecule?
Phosphorus trifluoride molecule consists of phosphorus as a central atom surrounded by three highly electronegative fluorine atom.
All three atoms of fluorine share one electron of phosphorus to complete their octet leaving behind one lone pair on phosphorus atom.
As per VSEPR theory, the repulsion caused among lone pair and bond pair generates a force that bends the P-F bonds towards the downward direction and makes it asymmetric.
The geometrical shape of the PF3 molecule formed is trigonal pyramidal. And all the P-F bonds have some non zero value of dipole moment.
The bond angle of (F−P−F) is approximately 96.3 degrees.
Due to the difference in the electronegativity of atoms (P and F) and trigonal pyramidal shape of molecules, the phosphorus trifluoride is a polar molecule.
Factors affecting polarity of a molecule
Electronegativity: The term electronegativity means the strength of an atom to attract the bonded pair of electrons towards it.
More electronegative atom attracts the bonded electrons pair with greater influence as compared to the lesser electronegative atom.
If there is a difference between the electronegativity of atoms, the polarity in such a molecule rises.
The polarity of a molecule is directly proportional to the difference between the electronegativity of atoms involved in that molecule.
Geometrical Structure: The molecules that are symmetrical in shape have zero dipole moment. It means the symmetrically shaped molecule is nonpolar in nature whereas asymmetric molecules are polar.
The molecules in which electronegativity of atoms are the same and have no lone pairs form the symmetrical shape.
Below is the image of the geometrical structure of phosphorus trifluoride.
Note: It must be understood that the symmetrical shaped nonpolar molecules can have a polar bond within it, but due to symmetrical geometrical shape the polarity of bonds gets canceled with each other resulting in a nonpolar molecule.
Dipole Moment: The dipole moment of a molecule is the measure of its polarity. The polarity of a molecule is directly proportional to its dipole moment.
Mathematically, it is the product of the charge on atoms and distance between them.
D = Q * R
Its SI unit is Debye, denoted by D.
The SI unit of PF3 is 1.03 D.
Properties of PF3
- Phosphorus trifluoride is a colorless and odorless gas at room temperature.
- In a gaseous state, its density is around 3.91 g/L.
- The melting point of this compound is −151.5 °C or −240.7 °F and its boiling point is −101.8 °C or −151.2 °F.
- This compound gets slowly soluble in water ie; undergo slow hydrolysis.
Uses of PF3
- This compound is widely used as a ligand in various metal complexes.
- Being ligand, in metal carbonyls, it parallels the CO molecules.
Phosphorus trifluoride is a chemical compound that has three fluorine atoms covalently bonded and one lone pair on phosphorus atom.
As per VSEPR theory, its geometric shape is trigonal pyramidal and due to differences in the electronegativity between P and F atoms, the P-F bond is polar.
And the entire molecule ensures non zero dipole moment.
Therefore the PF3 is a polar molecule.
So guys, if you have any questions regarding the non-polarity of PF3, you can ask them in the comment section. We will reach out to you as soon as possible.